This document discusses computational modeling of cyclones. It describes three turbulence models that can be used - the k-epsilon model, ASM model, and Reynolds Stress Model. It also outlines the key forces on particles in a cyclone - drag, centrifugal, and buoyant forces. The document shows the geometry and meshing of a cyclone in ANSYS and compares the results to a paper. The velocity and pressure profiles from ANSYS agree with the paper, but ANSYS could not capture the full volumetric results or negative pressure zone seen in the paper.

1. Computational Biomechanics
-Navid Allahverdi
CYCLONE THEORY
-Pritam Patil

2. Cyclone
• Rotational effects
and gravity
• Fluid flows in a
spiral pattern
• Heavier particles
have high inertia
• Strike the wall and
fall off
• Forced vortex
removes air from top

3. Models
• 1] k-έ model: It assumes isotropic turbulence, so
it is not suitable for the flow in a cyclone which
has anisotropic turbulence.
• 2] ASM model: It ignores the effect of stress
convention.
• 3] Reynolds’ Stress Model (RSM): It solves a
transport equation for each component of
Reynolds’ Stress.

4. 3 Forces on particles
• r(p) Radius of Particle
• ρ(f)  Density of Fluid
• ρ(p)  Density of particle
• r Rotational radius of the
particle in the cyclone.
• Fd Drag force
• Fc Centrifugal force
• Fb Buoyant Force

5. Geometry
• Sketch circles
• Skin/Loft
• Extrude

6. Meshing Error

7. Mesh Comparison
Paper ANSYS

8. Tree View

9. Velocity

10. Top View

11. Pressure Contours

12. Paper Results

13. Pressure
• Pressure decreases radially
from wall to centre and a
negative pressure zone
appears in forced vortex.
• The pressure gradient is the
largest along the radial
direction, as there exists a
highly intensified forced
vortex.

14. Tangential Velocity
• The value of tangential velocity
equals zero on the wall and the
centre of the field.
• The high speed fluid enters the
inlet and is accelerated up to
1.5-2 times the inlet velocity.
• Then the velocity decreases as
the gas spins down along the
wall.

15. Axial Velocity
• Forced vortex is a twisted
cylinder and not completely
axially symmetric, esp. in the
conical section.
• The forced vortex does not
coincide with the geometrical
centre of the cylindrical body
of the cyclone.
• The diameter of the forced
vortex is a little larger than
that of the vortex finder.

16. Radial Velocity
• The forced vertex in the centre
is a twisted cylinder.
• Its axis does not coincide with
the geometrical axis of the
cyclone and is not a line but a
curve.
• In the conical section, the
radial velocity is much larger
than that of the cylindrical
section..

17. Comparison
ANSYS Velocity Tangential Velocity

18. …….
ANSYS Pressure Static Pressure

19. Mass Flow Rate

20. Results
• 1] The geometry in Ansys is exactly similar to the one discussed in the paper.
• 2] CFX-mesh generated warnings and also the numbers of elements generated were very large.
• 3] Solver run almost took 2 hours to compile the results since the number of elements very large.
• 4] Boundary condition given at the inlet was Mass Flow Rate instead of the inlet velocity.
• 5] The results were obtained only on the surface and not over the entire volume.
• 6] Velocity results agree with the paper velocity results, i.e. Fluid are accelerated as it enters and the
velocity decreases as the fluid reaches toward the bottom of the cyclone.
• 7] Pressure results agree the paper pressure results, i.e. Pressure decreases radially from the wall toward
the centre however a negative pressure zone was not seen in the ANSYS results probably since the results
of the whole volume of the cyclone was not seen (or calculated by ANSYS)
• 8] But, Mass Flow Rate at the top surface was negative indicating that the velocity is in the opposite
direction demonstrating the formation of the forced

22. References
• Numerical study of a Gas-Solid flow in a cyclone
separator. (Wang et al) Dec 2003
• http://en.wikipedia.org/wiki/Cyclonic_separati
on